Optimization and characterization of laser cladding of NiCr and NiCr–TiC composite coatings on AISI 420 stainless steel

Abstract

AISI 420 Martensitic stainless steel is the major precursor for steam turbine blades. Under the operational conditions of the steam turbine, this steel undergoes erosion because of the impingement of water droplets. The aim of this research is the laser cladding of NiCr and NiCr–TiC powders and producing metal matrix composite NiCr–TiC on stainless steel substrate to enhance the rigidity and erosion resistance of AISI 420 stainless steel. The laser cladding was performed using pulsed Nd: YAG laser with concurrent powder injection. By setting the powder feeding rate, power, and laser scanning rate, the effect of each parameter on the laser cladding process was investigated and the optimal parameters for laser cladding were chosen. The elemental, phasic, and microstructural assessments and characterizations of the obtained coatings were done by optical microscope, scanning electron microscope, alongside energy dispersive spectroscopy (EDS), X-ray diffraction. It was observed that the structure of the clad from the interface upwards consists of cellular, columnar, and coaxial dendrites. It was also seen that the hardness of the composite clad containing reinforcement particles was far greater than that of cladding without such particles because of the increased effect of nucleation and the presence of TiC particles. It was also found that the weight loss of the composite clad of NiCr–TiC was less than that of NiCr and stainless steel substrate, while its erosion resistance was greater compared to NiCr and steel substrate.